U.S. patent number 5,308,981 [Application Number 07/872,693] was granted by the patent office on 1994-05-03 for method and device for infrared analysis, especially with regard to food.
Invention is credited to Peter Perten.
United States Patent |
5,308,981 |
Perten |
May 3, 1994 |
Method and device for infrared analysis, especially with regard to
food
Abstract
In analysis of a sample of unground grain, infrared light is
directed towards the sample and is detected after reflection on the
sample. For analysis of wheat, light wavelengths within the
interval 1050-1400 nm are used with a light detector of PbS-type. A
suitable infrared analyzer has a rotatable filter device (5) with a
plurality of filters (4) within the stated wavelength interval and
is disposed to be able to carry out in a short time period a large
number of measurements.
Inventors: |
Perten; Peter (12, CH-6055
Alpnach Dorf, CH) |
Family
ID: |
20382538 |
Appl.
No.: |
07/872,693 |
Filed: |
April 23, 1992 |
Foreign Application Priority Data
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Apr 23, 1991 [SE] |
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9101220-3 |
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Current U.S.
Class: |
250/339.11;
250/910; 250/341.8; 250/339.12; 250/358.1; 356/418 |
Current CPC
Class: |
G01N
33/10 (20130101); G01N 21/4738 (20130101); Y10S
250/91 (20130101); B07C 2501/0081 (20130101); G01N
21/3563 (20130101) |
Current International
Class: |
G01N
33/10 (20060101); G01N 33/02 (20060101); G01N
21/47 (20060101); G01N 21/35 (20060101); G01N
21/31 (20060101); G01N 021/35 () |
Field of
Search: |
;250/339,343,341,351,358.1 ;356/418 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Rosenthal, "Characteristics of Non-Destructive Near-IR Instruments
For Grain And Food Products", 1986 pp. 1-23. .
"Near-Infrared Reflectance Analysis", Analytical Chemistry, vol.
55, No. 12, Oct. 1983, By D. Wetzel, pp. 1165A-1176A..
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Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Dunn; Drew A.
Attorney, Agent or Firm: Young & Thompson
Claims
I claim:
1. A method of analyzing a sample (7) of grain comprising the steps
of;
a) directing infrared light of certain wavelengths toward the
sample,
b) detecting the infrared light by means of a photocell device (8)
after interaction of the infrared light with the sample,
c) using the detected infrared light to determine the relative
amount of certain substances in the sample, the improvement
comprising;
d) directing infrared light within the interval of 1050-1400 nm
toward a sample of unground grain,
e) detecting the infrared light which is reflected from the
unground grain,
f) analyzing the sample is done by generating an analysis value as
a mean value measurement wherein the results are obtained in
measurements of at least 30 different sample configurations.
2. Method according to claim 1, wherein the totality of the
measurements is carried out within 10 seconds.
3. Method according to claim 1, wherein analyzing the sample is
carried out while the sample is in movement relative to the
photocell device.
4. Method according to claim 1, wherein the light detecting is done
by a detector of lead sulphide type.
5. Method according to claim 1, wherein predetermined wavelengths
of 1128, 1138, 1154, 1188, 1200, and 1212 nm are used in analyzing
wheat.
6. Method according to claim 5, wherein wavelengths 1218, 1254, and
1320 nm are also used in analyzing wheat.
7. Method according to claim 1, wherein the grain is caused to move
downwardly along a vertical path during analyzing the sample.
8. In an infrared analyzer for determining relative amounts of
certain substances in a sample of unground grain, wherein between a
light source (2) and a sample container having a window (6), there
is arranged a filter device (5) from which only infrared light of
one specific wavelength at a time can reach the sample (7), and
there being a photocell device (8) for detecting light from the
sample; the improvement in which the photocell device (8) is
disposed between the filter device (5) and the sample (7) to detect
reflected light from the sample, the filter device (5) includes a
continuously rotatable disc, which is provided with a number of
different filters (4) to let light through in the interval
1050-1400 nm, in the photocell device (8) there is at least one
detector of lead sulphide type, and the analysis is disposed to
register measured values during rotation of the filter disc (5),
and means defined a vertical path for the grain along which path
the grain moves downwardly during analysis, said means having a
transparent window (6) through which the light passes from the
filter device (5) to the sample and from the sample to the
photocell device (8).
9. Infrared analyzer according to claim 8, wherein the filter
device (5) is provided with separate filters (4) for at least 1128,
1138, 1154, 1188, 1200, and 1212 nm.
10. Infrared analyzer according to claim 9, wherein in the filter
device (5) there is also included filters (4) for 1218, 1254, and
1320 nm.
Description
FIELD OF THE INVENTION
The present invention relates to a method of analysis of a sample,
especially a food sample, whereby certain wave lengths of infrared
light are directed towards the sample and after passage thereof are
detected by means of a photocell device to determine the relative
amount of certain substances in the sample. The invention also
relates to a device for carrying out said method.
BACKGROUND OF THE INVENTION
It is known to determine the chemical composition of a sample with
the aid of infrared analysis, whereby infrared light is either
reflected against a sample or is allowed to penetrate through a
sample. By measuring the amount of energy absorbed by the sample at
certain wave lengths, it is possible to determine the chemical
composition of the product. This is utilized in a variety of
different contexts, inter alia in the food industry, for product
analysis.
In the flour milling industry, it has been the practice for many
years to check the flour quality with the aid of infrared analysis
as described above, and in this case reflection analysis has been
used, i.e. reflected light from the sample has been measured.
It has, however, been a long felt need to be able to perform
effective and rapid analysis of unmilled grain, for the purpose of
better quality sorting of different shipments of grain. Tests have
shown that equipment which has, up to now, usually been used for
reflection analysis of flour, and in which light detectors of lead
sulphide type have been used, has not been usable for whole grain
analysis, since the signals obtained have proved to be too small in
order to be of any practical use. It has instead been suggested to
perform whole grain analysis by transmission measurement of wave
lengths of less than 1100 nm and using light detectors of silicon
type, see for example U.S. Pat. No. 4,286,237. One disadvantage is,
however, that analysis can only be performed on relatively thin
layers of grain, where the thickness does not exceed 25 or 30 mm.
It is also proved difficult to perform analysis on samples which
are in motion relative to the analysis equipment, i.e. to measure a
continuous flow of grain. Another disadvantage is that any
variations between a number of light sources used will affect the
measurements negatively.
SUMMARY OF THE INVENTION
The purpose of the invention is to make possible analysis of
unground products, such as grain, in a more simple, better and more
rapid manner than previously.
This purpose is achieved in a method according to the invention by
virtue of the fact that detection is carried out on reflected light
from a sample of unground grain, that light wave lengths within the
interval 1050-1400 nm are used, and that an analysis value is
created as a mean value of measurement results obtained in
measurements of at least 30 different sample configurations.
According to the invention, it is of advantage that the
measurements be carried out within 10 seconds. Analysis can thus be
carried out while the sample is in movement relative to the
analysis equipment. It is especially suitable for light detection
to use a detector of lead sulphide type.
An infrared analyzer of the type to which the invention relates and
which is designed for determining the relative amounts of certain
substances in a sample, especially a food sample, is constructed
such that between a light source and a sample container, there is
arranged a filter device from which only infrared light of one
specific wave length at a time can reach the sample, there being a
photocell device for detecting light from each sample. This
infrared analyzer is characterized according to the invention in
that the photocell device in a known manner is disposed between the
filter device and the sample to detect reflected light from the
sample, that the filter device includes a continuously rotatable
disc which is provided with a number of different filters to let
light through in the interval 1050-1400 nm, that in the photocell
device there is at least one detector of lead sulphide type, and
that the analyzer is disposed to register measured values during
rotation of the filter disc.
It has proved possible through the invention by using somewhat
different wavelengths than those which could be used previously for
reflection analysis of flour, to be able to carry out analysis of
unground grain. Possibilities have thus been opened for rapid and
simple quality sorting of grains in a manner which was not possible
previously immediately upon taking delivery of the grain.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be explained below in more detail with the aid
of an example, shown schematically in the accompanying drawing, of
an infrared analyzer according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
An infrared analyzer 1 according to the invention and shown in the
drawing has a light source 2, which, via an optical system 3, emits
light towards a filter 4 in a filter disc or filter device 5
provided with a number of monochromatic filters. This filter disc
is rotatable so that one filter at a time can be subjected to
light. By virtue of the fact that the filters are adapted to permit
passage of different specific wavelengths, depending on the filter
used, be directed to a window 6 of a sample container, behind which
where is a sample 7 of unground grain which is possibly in
movement, suitably vertically.
Reflected light from the sample 7 photocell device or light
detector 8, which is located relatively near to the window 6 but to
one side of the beam 9 striking the window 6 perpendicularly. This
light detector 8 is of PbS-type and can be placed with advantage so
that it is struck by rays which are reflected at an angle .alpha.
from the incident beam 9. The angle .alpha. can with advantage be
about 45.degree.. Additional light detectors 8 distributed about
the light beam 9 are also possible.
The filter disc 5 is continuously rotatable by means of a motor 10
and has the filters 4 placed with such circumferential spacing that
only one filter at a time can be subjected to light. The spacing
between the filters should be at least one filter diameter.
Radially outside the filters 4, the filter disc 5 is provided with
a number of uniformly spaced apertures 11. During the rotation of
the filter disc, these apertures 11, which suitably have the shape
of radially extending slots, pass a positional sensor 12 securely
mounted in the analyzer 1, to thereby make it possible to sense the
current rotational position of the filter disc. The positional
sensor 12 consists of a detector fork of the type where a light
source and a light detector are on either side of the filter disc 5
and can thus indicate each aperture 11 which passes. By registering
the signal from the light detector 8 at certain rotational
positions of the filter disc 5 (determined with the aid of the
positional sensor 12), it is possible, with the sufficient number
of apertures 11, to, under one rotation of the filter disc, to
register at least one signal reading from the light detector 8 for
each filter 4. Instead of being reflected against the sample 7,
light can be reflected in a well-known manner at selected occasions
against a reference surface 13, which can be swung into the beam of
light 9 when a suitable filter is illuminated.
When measuring reflected light from a sample consisting of whole
grains of wheat, poor reproducability was obtained between the
individual tests, due to how the grains of wheat happened to be
oriented in each individual test. By making measurements of many
tests, however, i.e. with many different configurations of wheat
grains, and by computing mean values of these many measurements, it
has proved possible to achieve a good accuracy of analysis, with a
standard deviation within 0.1-0.2%.
In order to reduce purely electronic measuring errors, it has
proved suitable, for each sample configuration, to generate the
measurement results for the different filters as the mean value of
a number of individual measurements, i.e. measurements for several
rotations of the filter disc 5, e.g. two, four, six or more
rotations per configuration. By allowing the filter disc 5 to
rotate rapidly, i.e. 25 rps, it is possible to make at least 25
measurements per second for each filter. If the number of apertures
11 is great in relation to the number of filters 4, there will be a
plurality of possible measuring points for each filter,
representing different measurement locations for each filter. It
will thus be possible to calculate a mean value for each specific
measuring location on each filter, thus making it possible to
reduce the effect of variations in the local transmission of the
different filters.
The great rapidity of measurement described above makes it possible
to make sufficiently many measurements even for samples in motion
relative to the window 6, presupposing of course that the movement
is not all too rapid.
It has proved possible according to the invention with a light
detector 8 of PbS-type to carry out analysis of unground grain by
using absorption bands within the wavelength interval 1050-1400 nm.
An especially advantageous wavelength combination has proved to be
1128, 1138, 1154, 1188, 1200 and 1212 nm. This combination has made
it possible to analyze the content of protein, water, starch and
fat in whole grains of wheat. In addition to the wavelenghts
mentioned, it is also possible with advantage to use the
wavelengths 1218, 1254 and 1320 nm to refine the analysis.
As was mentioned above, a number of measurements are made for each
filter against a reference and against different samples. After
converting the signal amplitudes measured from analog to digital
form in an A/D converter, the mean value R.sub.m is computed from
the reference signal amplitudes and the mean value P.sub.m of the
sample signal amplitudes. Thereafter, there is computed the
logarithm for the quotient R.sub.m /P.sub.m for the filter in
question, i.e. for the quotient (R.sub.m /P.sub.m).sub.i where the
index i indicates which filter is intended. This is done in a
processor coupled to the light detector 8 and the position
indicator 12.
It has been shown that the deviation between different samples will
be relatively great when the particle size in the sample exceeds
about 1 mm, and increases with increased particle size, due inter
alia to the fact that there will then be relatively much air
between the particles (the cereal grains). In order to improve the
reproducability between different subsamples with large particles,
a correction is suggested of the measured value in accordance with
the following: ##EQU1##
Here Ref 1 represents a first reference filter with a low
wavelength, and Ref 2 represents a second reference filter with a
high wavelength. These two wavelengths are selected so that they do
not provide any absorption for those components which one is
measuring for. The first, low reference wavelength can, for
example, at an absorption interval of 1100-1250 nm, be 1077 nm
while the other, higher reference wavelength can be 1280 nm.
Normally, the value (R/P).sub.Ref 1 is significantly less than the
corresponding value (R/P).sub.Ref 2, which will mean that the
formula, at low values of (R.sub.m /P.sub.m).sub.i, will give a
value close to zero, but for high values of (R.sub.m
/P.sub.m).sub.i, will have a value close to 1. This correction
means that for large particles, there will be a uniform scale where
the value curve goes through the origin and the value one. Finely
ground samples do not have the same need for correction.
The percentage of protein in grain can be determined by a formula
of the type
where i is the number of filters and k.sub.0 . . . k.sub.i are
constants, which are determined according to the least squares
method. For large particles, the terms involved are corrected
according to the above, i.e. the log values are replaced with log'
values.
The infrared analyzer 1 according to the invention is of course
enclosed in a manner not shown in a case so that outside light
cannot affect the measurements. The principle of a reflection
analyzer is described in detail in, inter alia, U.S. Pat. No.
4,479,055 and is well known among persons skilled in the art.
The number of filters 4 in the filter disc 5, as well as the
wavelength ranges for the filters, can of course be varied as
needed, depending on the type of grain or other unground product
which one desires to analyze.
* * * * *